Chemical method! We will use for that the sulphuric acid 28° baumés. Attention with projections! Wear gloves rubber, glasses, protective apron. It is initially necessary to begin a traditional work of approach (graver + cutter). The goal is to release the gangue with nearest possible test (shell) without never touching it with the tool. The less thick the layer remaining to be attacked by the acid will be, the better the action will be precise and short. One should not lose sight of the fact that the surface of the shell is always furrowed many cracks. If the action of the acid is too long, then this one infiltrates under the shell by causing cracks weakening the fossil. Thus it is to better spend a little more time to this mechanical approach. That requires precision and patience. But it is worth while. This work of approach ' fin' will also enable you to locate the badly fossilized zones (fractured shell, non-existent umbilical point, etc...). If you note too many "lacks", finish the release with the hand (cutter, scraper). The acid would do nothing but accentuate these "lacks".

Let us suppose that you have the ideal fossil, too not fissured. You released it as in the photograph opposite.

Start by posing a pad of adhesive ' scotch' (or equivalent) around the umbilical point, behind the top of the coasts. That will enable us to form a kind of well to store a spoon of acid preventing this one of épancher towards outside by capillarity (If not, in a few minutes the acid is spread out outside, dried quickly without acting or almost. In more the places having dried quickly with the air stain of an indelible color ' rouille'!

Let act a good day, with the shelters of the heat, draughts, by supervising the level of the liquid to avoid any drying. Caution! Do not do that in the apartment or a part where you live. The acid which evaporates is dangerous for your lungs in a closed space.

At the end of one or two days, rinse abundantly with water, and check the result. If it remains still much of gangue and that the cracks are very few, you can remake a second bath of acid. But to think of drying the front fossil well. Reinforce possibly the pad of adhesive so necessary.Then, remove the pad of adhesive (in general it is rather easy).

Then, to make the periphery of the ammonite, It is necessary to find a means of making act the acid without it evaporating wildly. It is the absorbent cotton which will be our saver! Moisten it of acid and cover surface with the ammonite. Let act one day like previously by sprinkling cotton from time to time.

Here, opposite, the result before and after rinsing. Not badly! Not? ... It any more but does not remain to rinse abundantly with water. Do not hesitate to let soak the fossil several days in a water container which you often renew. Then, there will remain to you the completion of the recalcitrant zones to the cutter and the scraper.

Final result below.....